In most cases, a manufacturer who produces and distributes a product makes a production plan on the basis of a distant future shipment plan that is preliminarily formed by the sales side, and accordingly actual production is carried out. Ideally, if all of requested amount is produced just before shipment and sales, followed by actual shipment and sales, it is possible to avoid opportunity loss due to emergence of shortage, and occurrence of surplus stocks. In a real field, however, production is made earlier than a scheduled shipment time, inmost cases, taking production capacity and transportation lead time into account. In particular, according to market globalization of recent years, exports from one base to worldwide markets are increasing, and it becomes more and more important to contrive how a production is made advance in time, in order to export a right amount at a right timing to each location.
It is effective to begin production advance in time to avoid being out of stock due to deficiency in supply. However, there is a hidden possibility that if a shipment plan of the product already manufactured is downwardly revised because of market trend change, the product already manufactured will be built up as surplus stocks.
In view of the situation above, the technique described in the following patent document 1 makes a production plan considering demand certainty, thereby avoiding out-of-stock state, and simultaneously preventing the probability of surplus stock occurrence. Specifically, in the patent document 1, priorities are assigned to each of sales sources, and high priority is placed on demand information from the sales source to which high priority is assigned, and a production plan is made accordingly.